Vector network analyzers (VNAs) are used to measure the performance of many types of electrical systems. However, conventional VNAs are subject to measurement errors. Prior to using a conventional VNA, it is necessary to calibrate the VNA to account for any measurement error so as to ensure an accurate measurement. In order to ensure the accuracy of the calibration over a wide frequency range, up to twenty calibration standards may need to be measured.
Historically, mechanical standards were used to calibrate a VNA. A number of mechanical standards are required to be measured individually on the VNA, making it necessary to physically perform each mechanical standard. In particular, it is necessary to physically connect and disconnect the mechanical standard to the VNA for each measurement. Typically, it takes 15-20 minutes to calibrate a VNA using mechanical standards. Due to the amount of time it takes to mechanically calibrate a VNA, particularly in relation to how long it takes for the VNA to measure devices, it is highly desirable to reduce the calibration time.
In order to reduce the time required to calibrate a VNA, electronic calibration has replaced physical calibration for many applications. Electronic calibration devices take several impedance standards with different electrical characteristics, and places them within a module having an electronic switch for switching between the standards. These impedance standards can be mechanical standards or other known impedance devices. Typically, the electronic calibration device only needs to be physically connected to the VNA once. The electronic calibration device then switches all necessary or desired calibration standards to the VNA test ports.
Currently, semiconductor based or solid state electronic calibration devices are available for calibrating VNAs operating at frequencies of substantially 300 kHz to 9 GHz for low frequencies devices and substantially 45 MHz to 26.5 GHz for higher frequency devices. Mechanical switch based electronic calibration devices exist that can operate up to 40 GHz. However, mechanical switches are much slower and less repeatable than solid state switches.
At high frequencies, current electronic calibration devices become unstable, and are thus not usable for calibrating VNAs. In order to provide an electronic calibration device that is operable at high frequencies it has been proposed to insert an iron-embedded epoxy, such as poly-iron, into the cavity of the electronic calibration device to suppress mode excitation. However, when cycled over time and temperature variation, the mode suppression varies. Thus, electronic calibration devices with poly-iron infused cavities are not stable for use in calibration.
As a result of various technological advances and the requirement for increased bandwidth, a vast number of electronic devices operate at frequencies within the range of substantially 26.5 GHz to upwards of 67 GHz. There are VNAs that operate within this range for performing vector analysis on devices operating at high frequencies. In order to calibrate a VNA using mechanical standards for operating at frequencies of greater than 40 GHz, it is necessary to physically calibrate the VNA, individually measuring each mechanical standard. As described above, physically calibrating a VNA using mechanical standards is labor intensive and time-consuming.